The determination of particle size distributions of liquid samples is necessary in pharmaceutical, life-science, and environmental-science applications, among others. The liquid samples may include dispersed particles of sizes ranging from less than 0.1 μm to 1000 μm. Generally, different types of particle analyzer are used to determine the sizes of particles of different size ranges.
Bright-field imaging particle analyzers may be used to determine the sizes of particles larger than about 0.5 μm in a liquid sample. For example, micro-flow imaging (MFI) particle analyzers are described in U.S. Pat. No. 7,064,826 to Rabinski, et al., issued on Jun. 20, 2006, in U.S. Pat. No. 7,217,937 to King, issued on May 15, 2007, in U.S. Pat. No. 7,307,721 to King, issued on Dec. 11, 2007, in U.S. Pat. No. 7,379,577 to King, et al., issued on May 27, 2008, and in U.S. Pat. No. 7,605,919 to Oma, et al., issued on Oct. 20, 2009, which are incorporated herein by reference. Other examples of bright-field imaging particle analyzers are described in U.S. Pat. No. 6,061,130 to Plate, et al., issued on May 9, 2000, and in U.S. Pat. No. 6,522,781 to Norikane, et al., issued on Feb. 18, 2003, which are incorporated herein by reference. By using such particle analyzers, particles of an upper size range in a liquid sample can be individually analyzed and visualized.
On the other hand, a dark-field imaging particle analyzer may be used to determine the sizes of particles smaller than about 1 μm in a liquid sample. For example, nanoparticle tracking analysis (NTA) particle analyzers are described in U.S. Pat. No. 6,280,960 to Carr, issued on Aug. 28, 2001, and in U.S. Pat. No. 7,399,600 to Carr, issued on Jul. 15, 2008, which are incorporated herein by reference. By using such particle analyzers, particles of a lower size range in a liquid sample can be individually analyzed and visualized. However, as NTA requires the capture of several dark-field image frames, the rate of analysis is relatively low.
Although both bright-field and dark-field imaging particle analyzers are separately known, the use of different particle analyzers to determine the sizes of particles of an upper size range and particles of a lower size range in the same liquid sample is highly inconvenient. Furthermore, the sizes determined by the different particle analyzers often disagree where the upper and lower size ranges overlap.
An imaging flow cytometer combining bright-field and dark-field imaging is described in U.S. Pat. No. 7,634,125 to Ortyn, et al., issued on Dec. 15, 2009, which is incorporated herein by reference. This imaging flow cytometer may be used to determine the sizes of cells in a liquid sample. However, cells of only a narrow size range, typically, about 5 μm to 15 μm, can be individually analyzed and visualized.
A particle analyzer combining bright-field imaging and laser-diffraction analysis is described in U.S. Pat. No. 7,471,393 to Trainer, issued on Dec. 30, 2008, which is incorporated herein by reference. This particle analyzer may be used to determine the sizes of particles of an upper size range and particles of a lower size range in a liquid sample. However, the particles of the lower size range cannot be individually analyzed or visualized. Rather, the particles of the lower size range are analyzed as an array, on the basis of their laser diffraction pattern.
Particle analyzers combining single-particle light-extinction and light-scattering analysis are described in U.S. Pat. No. 5,835,211 to Wells, et al., issued on Nov. 10, 1998, and in U.S. Pat. No. 6,794,671 to Nicoli, et al., issued on Sep. 21, 2004, which are incorporated herein by reference. These particle analyzers may be used to determine the sizes of particles of an upper size range and particles of a lower size range in a liquid sample. However, the size determination relies on a calibration curve determined by using external calibration standards and is prone to calibration errors arising from differences between the optical properties of the particles and the calibration standards. Moreover, the particles cannot be individually visualized.
Therefore, a particle analyzer combining bright-field and dark-field imaging that allows particles of an upper size range and particles of a lower size range in a liquid sample to be individually analyzed and visualized is highly desirable. Such a particle analyzer should provide consistent sizes throughout the upper and lower size ranges to enable a broad particle size distribution of the liquid sample to be accurately determined.